1. Field of the Invention
The present invention relates to photoelectric conversion devices and semiconductor devices having the same. In particular, the invention relates to a photoelectric conversion device having thin film semiconductor elements and a method of fabricating the same. Further, the invention also relates to an electronic device having such a photoelectric conversion device.
2. Description of the Related Art
There are known numerous photoelectric conversion devices that are used generally for detection of electromagnetic waves. For example, photoelectric conversion devices that detect ultraviolet rays to infrared rays are collectively referred to as photosensors. Among them, photosensors that detect visible light in the wavelength range of 400 to 700 nm are particularly referred to as visible light sensors. Many of such visible light sensors are used for devices whose illuminance and on/off switching need to be controlled in accordance with the living environment of humans.
In particular, a photosensor used for a display device detects the surrounding luminance of the display device and controls the luminance to be displayed on a panel. This is in order to reduce excess power consumption by detecting the surrounding luminance and determining an appropriate luminance to be displayed on the panel. Such a photosensor used for controlling luminance is applied to mobile phones or personal computers, for example.
Further, such a photosensor detects not only the surrounding luminance but also the luminance of a backlight of a display device, in particular, a liquid crystal display device, so that the luminance of a display screen can be controlled.
In such a photosensor, a photodiode is used in a detection unit, and an output current of the photodiode is amplified with an amplifier circuit. As such an amplifier circuit, a current mirror circuit is used for instance (e.g., see Japanese Patent No. 3444093, U.S. Pat. No. 5,936,231). The amplifier circuit is constructed from thin film transistors (TFTs).